Sheet-metal screw cap for a container



Oct. 13, 1970 J, VAN D GRLJN 3,533,527

SHEET-METAL SCREW CAP FOR A CONTAINER Filed Dec. 13, 1967 2 Sheets-Sheet 1 INVENTOR L/OHAN mum 6P/J/v 1970 J. VAN DER GRIJN 33,527

SHEET-METAL SCREW CAP FOR A CONTAINER Filed Dec. 1.;5, 1967 2 Sheets-Sheet 2 FEQc/ o I I Fl (as 9 *INVENTOR JOHAN MN on 64mm A ORNEY United States Patent 01 free 3,533,527 Patented Oct. 13, 1970 SHEET-METAL SCREW CAP FOR A CONTAINER Johan van der Grijn, Deventer, Netherlands, assignor to Thomassen & Drijver-Verblifa N.V., Deventer, Netherlands, a Dutch limited-liability company Filed Dec. 13, 1967, Ser. No. 690,331 Claims priority, application Netherlands, Dec. 22, 1966,

6 18005 Int. Cl. B65d 41/04, 41/06 US. Cl. 215--43 2 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a sheet-metal screw cap for a container, more particularly a glass jar or bottle, Whose cylindrical mouth is formed externally with screwthreaded portions of predetermined pitch, the cap comprising. a cover and a cylindrical, downwardly directed rim whose lower edge is curled upward and inward, the curled portion being formed with screwthreaded portions associated with the screwthreaded portions of the container. In caps of the kind specified the upwardly and inwardly curled part has a considerable axial length, so that screwthreaded portions of adequate length can be obtained. Moreover, the considerable length means that the cap must be made from a flat disc of adequate diameter.

According to the invention, which relates to a screw cap of the kind specified, the amount of material used can be reduced while at the same time ensuring that the screwthreaded portions of the cap engage satisfactorily with the screwthreaded portions of the container, so that the torque which must be exerted on the cap when the container is closed is not excessive (an important point when the caps are used in automatic filling and sealing machines), while the manual torque which must be exerted to release the cap is neither excessive, nor inadequate. The latter requirement must be met to prevent the cap from being released too readily. Moreover, in this context it should be noted that fairly long screwthreaded portions more readily produce an adequate resistance torque for cap release than shorter screwthreaded portions.

Starting from the prior art sheet-metal screw cap of the kind specified, according to the invention each screwthreaded portion of the cap has a part over which the pitch is smaller than normal. Preferably, the pitch of the part having a smaller pitch decreases substantially to zero. When a cap of the kind specified is screwed tight, the afore-mentioned part of each screwthreaded portion is somewhat resiliently deformed by the associated screwthreaded portions of the container which have the aforementioned predetermined pitch, so that the torque requirements can be more readily met, even with the use of fairly short screw threaded portions. Since fairly short screwthreaded portions can be used, therefore, a considerable amount of material can be saved in comparison with the prior art caps, while screwing up and releasing the cap are brief operations.

Preferably, a screw cap according to the invention is manufactured by the performance of a method according to the invention, in which the screwthreaded portions are obtained by the deformation of a peripherally extending, inwardly directed curl, originally substantially circular in cross-section, on the lower edge of the afore-mentioned rim, although that part of each screwthreaded portion which is bounded by two deformed screwthreaded parts is not deformed. This step produces in a very simple and convenient manner a part of each screwthreaded portion having a smaller pitch, which can decrease substantially to Zero.

The applicants have discovered from tests that if the screwthreaded portions are simply produced in an in wardly directed curl of substantially circular cross-section, there is a risk that the lower edge of the cap will have a less satisfactory shape and show undulations indicating that the lower edge is no longer in a plane surface. To obviate this disadvantage, according to the invention, the radius of curvature of the lowest part of the curl is reduced before the screwthreaded portions are produced in the curl. The part having the reduced radius of curvature then forms a rigid whole protecting the cap against undesirable deformation during the subsequent production of the screwthreaded portions. Another advantage of this step is that the cross-section dimensions of each screwthreaded portion can be kept within close tolerances at all places. This is a very important feature in the manufacture of screw caps of the kind specified, in view of the tolerance demands made by consumers.

Preferably, according to the invention, the deformation of the curl, to obtain the screwthreaded portions, is performed by means of a radially expanding forcing device subdivided into sectors, the radial gaps between the sectors meeting the undeformed part of each screwthreaded por tion. A resulting advantage is that even if the radial gaps of the expanded forcing device are very wide in the immediate vicinity of the cap, no faults are caused in its screwthreaded portions. When a forcing device of the kind specified is used, the cap must be received with a close fit in a bowl-shaped matching container.

An embodiment of the invention is illustrated in the drawings.

The complete process for obtaining a screw cap according to the invention, starting from a fiat plate, can be divided into five stages, as shown in the drawings.

In the first stage (FIG. 1) a round, flat sheet-metal disc, more particularly made of possibly decorated or lacquered tin or aluminium plate, is deformed by deep drawing (see FIG. 1), thus producing a closed cover 1 and a cylindrical,

downwardly directed rim 2 on the cap.

In the second stage (FIGS. 2 and 2a) the lower edge 3 of the cylindrical portion 2 is slightly curved inwards, for instance by means of forcing rollers, to prepare the curled portion.

In the third stage (FIGS. 3 and 3a) the lower edge of the cap rim 2 is formed with an inwardly directed curled portion 4 of substantially circular cross-section, for instance by means of a curling punch.

In the fourth stage, as shown in FIG. 4 (a plan view from below) and in FIGS. 4a and 5, a suitable punch is used to reduce the radius of curvature of the lower portion 5 of the curled portion 4.

In the fifth stage (FIGS. 6 and 7) the curled portion 4 is deformed, to obtain three screwthreaded portions 7, 8 and 9, by means of a radially expanding forcing device subdivided into three sectors, the radial gaps between the sectors meeting the undeformed part of the screwthreaded portions 7, 8 and 9. During the operation of the expanding forcing device, the cap received in a bowl-shaped matching container can also be used in the third and fourth stages.

FIG. 8 shows a portion of the resulting three screwthreaded portions 7, 8 and 9, and

FIG. 9 is a graph showing the value of the variable pitch used according to the invention, in the longitudinal direction of each screwthreaded portion.

What I claim is:

i. A sheet metal screw cap for a container having a cylindrical mouth which is externally provided with screw; threaded sections with a predetermined pitch, said screw cap comprising a cover and a cylindrical downwardly directed rim, an inwardly and upwardly curved bead integral with the lower edge of said rim and provided with screw threaded sections on the inner side thereof, each screw threaded section of the bead having in its unassem-' bled free form an upper end portion and a lower end portion joined by an intermediate portion, said upper and lower end portions each having a pitch corresponding to said predetermined pitch on the screw threaded sections of said container, said intermediate portion having a smaller pitch decreasing substantially to zero.

2. The method of manufacturing a screw cap for a glass container having a cylindrical mouth provided with external threads of predetermined pitch which comprises the steps of forming a cap of generally cup-shaped form having a cylindrical side wall presenting a free edge, curling said free edge inwardly to present a continuous generally tubular bead, decreasing the radius of the lowest part of said bead where it meets said side wall, and then deforming said bead to present screw threads therein each having a lower major portion thereof equal in pitch to said predetermined pitch and an upper portion of less pitch than said predetermined pitch.

References Cited UNITED STATES PATENTS 1,667,003 4/1928 Hardiman 215-43 1,260,376 3/1918 Hammer 21543 1,308,745 7/1919 Hammer 215-43 WILLIAM T. DIXSON, JR., Primary Examiner US. Cl. X.R.

l1312l; 2l544; 220-39, 40 

